摘要:

The Canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the Canadian Liquefaction Experiment (CANLEX). The main objective of the project was to study the phenomenon of soil liquefaction, which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations. In many areas of Canada, large structures are constructed on or comprise sandy soils, e.g., some major hydroelectricity earth dams and many tailings impoundments in the mining industry. The behaviour of loose sandy soils can be difficult to predict, but can have a significant financial impact on these types of engineering structures. Consequently, the intent of the CANLEX project was to improve the overall understanding of soil liquefaction. This paper provides an overview of the CANLEX project, outlining the project objectives, major achievements, and conclusions. Four companion papers describe different aspects of the project; thus, together, the five papers provide a summary of the CANLEX project.Key words: geotechnical, liquefaction, CANLEX, collaborative project.

ISSN:0008-3674    

DOI:10.1139/t00-043

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

One of the primary objectives of the Canadian Liquefaction Experiment (CANLEX) project was to evaluate in situ testing techniques and existing interpretation methods as part of the overall goal to focus and coordinate Canadian geotechnical expertise on the topic of soil liquefaction. Six sites were selected by the CANLEX project in an attempt to characterize various deposits of loose sandy soil. The sites consisted of a variety of soil deposits, including hydraulically placed sand deposits associated with the oil sands industry, natural sand deposits in the Fraser River Delta, and hydraulically placed sand deposits associated with the hard-rock mining industry. At each site, a target zone was selected and various in situ tests were performed. These included standard penetration tests, cone penetration tests, seismic downhole cone penetration tests (giving shear wave velocity measurements), geophysical (gamma-gamma) logging, and pressuremeter testing. This paper describes the techniques used in the in situ testing program at each site and presents a summary and interpretation of the results.Key words: CANLEX, in situ testing, shear wave velocity, geophysical logging, pressuremeter.

ISSN:0008-3674    

DOI:10.1139/t00-044

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

One of the primary objectives of the Canadian Liquefaction Experiment (CANLEX) project was to develop and evaluate undisturbed sampling techniques as part of the overall goal to focus and coordinate Canadian geotechnical expertise on the topic of soil liquefaction. Six sites were selected by the CANLEX project in an attempt to characterize various deposits of loose sandy soil. The sites consisted of a variety of soil deposits, including hydraulically placed sand deposits associated with the oil sands industry, natural sand deposits in the Fraser River Delta, and hydraulically placed sand deposits associated with the hard-rock mining industry. At each site, a target zone was selected and various methods of ground sampling were performed. These included ground freezing and sampling, fixed piston tube sampling, Christensen double-tube core sampling, large-diameter sampling using the Laval sampler, and sonic (rotary-vibratory) continuous coring. Ground freezing and sampling was performed at all six sites; the other methods were used at only some sites. Geophysical (gamma-gamma) logging was also performed in boreholes near the freeze pipe to independently measure in situ void ratios. This paper describes the techniques used in the ground-freezing and various sampling programs and presents a summary of the results. Comparisons of void ratios measured for various types of samples and using geophysical logging are also made.Key words: CANLEX, ground freezing, sampling, geophysical logging, void ratio.

ISSN:0008-3674    

DOI:10.1139/t00-045

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A major aim of the Canadian Liquefaction Experiment (CANLEX) was to verify analysis procedures for predicting liquefaction phenomena. Towards this purpose, two loading events were carried out: a field event comprising a clay embankment built over a loose sand foundation layer, and a centrifuge test performed on a model of a sand embankment structure. Both the field event and the centrifuge model were planned so as to induce a static liquefaction failure and were instrumented to observe their response in terms of displacement and pore pressure. The fundamental mechanical characteristics of the foundation layer were determined from laboratory element tests (triaxial and simple shear). These tests formed the basis for the stress-strain modelling used in the numerical analyses. Two fundamentally different modelling techniques were used. One involved a fully coupled plasticity model, and the other involved a model based on a collapse-surface approach. The model and prototype structures were then analyzed and the predicted results in terms of displacements and pore pressures were compared with the measured values. The results from both approaches were found to be in reasonable agreement with the measurements, provided allowance was made for direction of loading and drainage effects were accounted for.Key words: liquefaction, field experiment, embankment, centrifuge model, elastic-plastic model.

ISSN:0008-3674    

DOI:10.1139/t00-042

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The Canadian geotechnical engineering community has completed a major collaborative 5 year research project entitled the Canadian Liquefaction Experiment (CANLEX). The main objective of the project was to study the phenomenon of soil liquefaction, which can occur in saturated sandy soils and is characterized by a large loss of strength or stiffness resulting in substantial deformations. The intent of this paper is to compare, interpret, and summarize the large amount of field and laboratory data obtained for six sites in Western Canada as part of the CANLEX project. The sites are compared in terms of both flow-liquefaction and cyclic-softening considerations. The paper presents a number of conclusions drawn from the project as a whole, in terms of both fundamental and practical significance.Key words: sand, flow liquefaction, cyclic softening, CANLEX.

ISSN:0008-3674    

DOI:10.1139/t00-046

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Liquefaction phenomena in saturated sands are examined. Fundamental factors that influence liquefaction susceptibility are considered from the background of comprehensive experimental evidence from test results on reconstituted specimens. These include those related to the loading system characteristics which do not enable measurements of the true post-peak behaviour. In particular, several issues related to the influence of initial state variables, on which there appears to be a lack of consensus in the literature, are dealt with. It is shown that at identical initial void ratio - effective stress state, undrained (constant volume) behaviour is profoundly affected by the fabric that ensues upon sample reconstitution. Very loose moist-tamped states are unlikely to be accessible to in situ sands. The susceptibility to liquefaction, both static and cyclic, is not only dependent on the initial state variables, but is also strongly affected by the effective stress path during undrained shear. Comparative tests on undisturbed samples retrieved by in situ ground freezing and their reconstituted counterparts show that water-pluviated specimens closely mimic the behaviour of in situ sands. Very small expansive volumetric strains due to pore-pressure gradients during short-duration loading, or after its cessation, could transform a sand into a strain-softening type, which otherwise would be dilative if completely undrained.Key words: anisotropy, laboratory tests, liquefaction, sampling, sands, shear strength.

ISSN:0008-3674    

DOI:10.1139/t00-040

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A thermomechanical model for saturated clays is proposed within the framework of recent extensions of the Cam-Clay model. The results of some tests found in the literature are analyzed, and the main features of the thermomechanical behaviour of clays are identified. The effect of the overconsolidation ratio (OCR) on the volume change of a soil (expansion-contraction) submitted to heating is well established using experimental data obtained for selected soils by various authors. However, existing models need to be modified to correctly model this feature. For this reason, a new volumetric thermal plastic mechanism is developed that allows for the prediction of plastic strains at higher OCR values. The overconsolidation effect observed when heating a normally consolidated soil is also modelled. Particular attention is paid to the coupling and hardening phenomena related to the combined effects of stress and temperature. A qualitative validation is made by examining the response of the model under a given thermomechanical path. Comparison with existing thermomechanical experimental results shows that the model can provide satisfactory predictions.Key words: clays, constitutive modelling, temperature effects, deformation, elastoplasticity, radioactive waste disposal.

ISSN:0008-3674    

DOI:10.1139/t99-111

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A study of land subsidence due to groundwater pumping in the city of Hanoi, Vietnam, was conducted by collecting and analyzing data on the geology, hydrology, soil properties, and observed settlements. The city of Hanoi is underlain by sediments consisting of organic and inorganic clays, silt, peat, sand, and gravel. The pumping of groundwater causes consolidation of compressible aquitard layers. The water demand for the city of Hanoi is increasing with time. The present total rate of water pumping is 450 000 m3/day, and there is a proposal to increase the rate to 751 000 m3/day by the year 2010. This research program involved the modelling of seepage related to pumping along with a stress-deformation analysis. The effect of surface infiltration was also modelled. The settlements computed for parts of the city of Hanoi were compared with measurements of settlement in the city area. The simulation results appear to be in fairly good agreement with the measurement results. The study showed that subsidence due to groundwater pumping is a serious problem in the city of Hanoi. It is important to continue to measure settlements and compute possible deformations associated with actual rates of pumping.Key words: subsidence, settlement, groundwater pumping, stress-deformation modelling, seepage modelling.

ISSN:0008-3674    

DOI:10.1139/t99-126

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

In this paper, the results of an experimental investigation of dynamic characteristics of gravelly cobble deposits, such as shear modulus (G) and damping ratio (D), are presented. The gravelly cobble deposits are very common in the Taichung metropolitan area of Taiwan where there is an urgent need to determineGandDfor dynamic analysis and design of structures. The test program includes measurements of shear wave velocity by the downhole method and large-scale dynamic triaxial tests and resonant-column tests. Special consideration is given to preparing samples of gravelly cobble deposits for laboratory tests. The "equal-weight replacement method" to scale down the real gravelly deposits to cell diameters is used for the preparation of samples. This method is found to be satisfactory, as consistent and reasonable results are obtained. The results of the present study show that the shear modulus - shear strain (G-&ggr;) relationship for this gravelly deposit does not follow exactly those reported in the literature. The deviation of thisG-&ggr; relationship from those reported in the literature is investigated and explained.Key words: shear modulus, damping ratio, downhole, shear wave velocity, gravel.

ISSN:0008-3674    

DOI:10.1139/t99-133

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The detection of shear zones along which a mass of soil is moving is essential for understanding the state of stability of natural slopes. Weaker zones in clay soils can be identified from low values of cone penetration test (CPT) tip resistance measured during penetration. This paper presents a case history illustrating the identification of softened shear zones in clay soils using the CPT and the observation of shear surfaces using continuous dynamic sampling (CDS). The analysis and interpretation of the CPT data are discussed in relation to the detection of shear surfaces using the CDS at a site with a history of slope instability. Difficulties encountered in identifying shear zones and detecting shear surfaces are discussed.Key words: cone penetration testing, slope stability, in situ testing, case history, shear zone.

ISSN:0008-3674    

DOI:10.1139/t99-129

出版商:NRC Research Press    

年代:2000

数据来源: NRC